Luminous compound and method of producing luminous objects therewith



Patented July 5, 1932 I UNITED STATES PATENT OFFICE HERMAN SCHLUNDT, OF COLUMBIA, MISSOURI, ASSIGNOR TO UNITED STATES RADIUM 'COBPORATION, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE LUMINOUS COMPOUND AND METHOD OF PRODUCING LUMINOUS OBJECTS THEREWITH N Drawing.

This invention relates to the use of radioactive luminous material and is concerned more particularly with a method of preparing such material and applying it in such manner that danger to the workmen is eliminated. The invention also comprehends a material suitable for such application.

It is well known that the handling and 0 application of radioactive materials, commonly used for rendering objects self-luminous, are likely tobe attended by harmful effects on the healthof the workmen. While these harmful .efi'ects are not thoroughly 5 understood and are likely to manifest themselves in many forms, such as anemia, it is known that such results are due to ingestion of radioactive luminous material by the workmen as Well as to exposure to radium 0 emanation and gamma rays emitted from radioactive luminous material. Ingestion of radioactive materials may be precluded by. the workmen taking proper precautions, while exposure to the emanation and 5 gamma rays emitted by such materials presents. a problem which has not heretoforebeen solved. In the form in which they are now used, these radioactive materials give off emanation and gamma rays at a definite 0 and fairly rapid rate: The gaseous emanation from a radioactive material can be confined if the material is hermetically sealed in a container, but in factories where luminous products are manufactured, it is customaryv for each workman to have before him, and removed from its container, a quantity of the radioactive material with which he is working. The emanation from the material consequently difluses through the room and in a room where a number of workmen are employed, the exposure to the emanation and the gamma rays from the different masses being used is such that in the course of time harmful results are likely to follow, regardless of'precautions that may be taken.

It isthe object of this invention to provide wa process of preparing and applying a radioactive luminous materialv under such conditions that exposure of the 'user to the emanation and gamma rays isjavoided and in ac- Application filed March 2?, 1929. W Serial No. 349,278.

cordance with this invention, a radioactive material is prepared under conditions such that its activity is practically nil or at least only a minor fraction of its equilibrium activity and the material is then applied to the object by the worlnnen during the period of low activity. When the material is treated in the manner presently to be described so that it is rendered substantially inactive, it can be handled and applied in the ordinary manner without danger to the worker, provided proper precautions against ingestion are taken, and the period of substantial inactivity is sufliciently long to permit it to be used for its ultimate purpose without difliculty.

In preparing the radioactive material, a soluble radium salt, such as radium bromide, is dissolved in water to make asolution of the desired concentration. The solution is then de-e'manated, which process can be carried on in numerous ways. For example, the solution may be boiled for a short time, such as five minutes, to cause the gaseous emanation to pass out of the solution and be difi'used into the atmosphere. Instead of boiling, the solution may be placed in a closed vessel and subjected to the action of a vacuum which removes the emanation from the solution, or

the emanation may be removed by bubbling air through the solution, the air entrapping the emanation and carrying it off. Other similar methods for removing the emanation may likewise be employed for the purpose, the methods above referred to being commonly practiced.

By removal of of the radium preparation is practically reduced to zero not considering the residual activity of radium A, radium B and radium C, which products decay in about three hours. During this three-hour period the emanation is building up slowly with the production of the decay products of rapid change, radium A, radium B and radium 0. However three hours after a radioactive solution has been eight hours 5.8% of the equilibrium amount the emanation the activity has accumulated, so that the substance during this period gives of]? little emanation as Well as gamma radiation.

Following the de-emanation treatment, a radioactiv'e sensitive compound, such as zinc sulphide, is added to the solution in a suitable amount, and the solution is then evaporated to dryness at a low temperature as, for example, from 100 to 110 C. The dry mass is then screened through bolting silk of 150 to 200 mesh and at once delivered to the workmen who are to use it. In applying the mixture, the workman mixes it with a suitable quantity, of a' vehicle, such as a water adhesive having gum arabic as a base, or an oil adhesive having rosemary oil as a base, to form a paint or paste which is then applied to the object by a brush, a stylus, or in some other ordinary way. In this mixture with a vehicle of radioactive and radioactive-sensitive compounds, the radioactive compound is temporarily substantially inactive, the period of inactivity continuing negligible for a number of hours, during-which the compound is to be applied to the object.

From the foregoing, it will be apparent that following the de-emanation treatment and the decay of radium A, B and C, the radioactive material does not give ofi in substantial amounts radium emanation and gamma rays which are harmful to the workmen. During this period of temporary substantial inactivity, the emanation builds up with the passage of time and as it is evolved radium C is produced and gamma rays emitted in an amount correspondingtothe amount of radium C present. For a period of hours, the radioactive material remains relatively inactive and at the expiration of about ten hours after the de-emanation treatment, the

. emanation may have increased to approximately 7%. During that period of hours, the emanation and gamma rays are given 01f in such small amounts that the effect of exposure to them is practically nil.

'So long as the mixture is applied during the period when it has only a small part of its normal activity with respect to alpha, beta and gamma rays, it may be handled without harmful effect and the time element is, therefore, an important feature of the invention. In order to obtain the advantages of'the new process, the preliminary treatment of the radioactive compound, the preparation of the mixture of the radioactive and radioactivesensitive compounds and the application of this mixture to the object must .be carried on within a fairly definite period of time, since otherwise the effect of the preliminary treatment is lost and the radioactive compound will regain its normal activity.

. While products which are givena coating of radioactive material in accordance with,

the process above set forth-do not have their final luminosity immediately upon their luminous objects, the radioactive material completion, this luminosity develops with the building up of the equilibrium products. The products consequently require aging fora period until radium C has developed in an amount suflicient to produce the desired effect. Ordinarily, this period may be a matter of a month, during which the products are gradually increasing in luminosity until the equilibrium point of the emanation is reached, and the maximum amount of radium C which gives of]? gamma rays is present. I

In the procedure heretofore followed in connection with the manufacture of selfemployed is at its maximum luminosity and the articles are ready for use as soon as finished. As a necessary incident to. attaining this result, the workers sufi'er dangerous exposure. While articles made by the present process require aging, this is not a matter of consequence as the aging takes place while the articles are in stock or in transit. At the same time the health of the workers is protected to an extent never possible with the prior practices.

The luminous compound-of the..invention is used for many purposes as, for example, for application to the dials of watches, clocks, aviation instruments, and the like.

What I claim is:

1. A method of producing luminous objects which comprises de-emanating a radioactive compound in solution and thereby renderingsaid compound temporarily substantially inactive, adding to the solution a radioactive-sensitive compound, recovering a mixture of said compounds from the solution and applying the mixture to the object while the period of temporary substantial inactivity of the radioactive compound continues.

2. A method of producing luminous objects which comprises de-emanating a radioactive compound in solution and thereby rendering said compound temporarily substantially inactive, the activity of said compound increasing with the passage of time following said de-emanation, adding to the solution of radioactive-sensitive compound, recovering a mixture of the compounds from the solution, and applying the mixture to the object before the activity of the radioactive compound has increased to a substantial no amount.

3. A method of producing luminous objects which comprises preparing a solution of a soluble radioactive salt, de-emanating the salt, adding a radioactive-sensitive salt to the 125 solution, evaporating the solution to dry ness at a relatively low temperature to produce a dry mixture of the salts in which the radioactive compound is temporarily subture to the object while the said period of 1 temporary substantial inactivity continues.

4. A method of. producing luminous objects which comprises preparing a solution of a radioactive salt, subjecting the solution to a treatment to de-emanate the solution, adding phosphorescent zinc sulphide to the solution, recovering the radioactive salt and the zinc sulphide from the solution in intimate mixture, and applying said mixture to the object while the radioactive salt is temporarily substantially inactive as a result of said de-emanating treatment.

5. A method of producing luminous 0bjects which comprises preparing a mixture of radioactive and radioactive-sensitive compounds, the emanation' from the radioactive compound being equal to a few per cent. of

the equilibrium amount of emanation but approaching said equilibrium amount with the passage of time, and applying said mixture to the object before the emanation increases to a substantial amount.

6. A method of producing luminous ob-' jects which comprises de-emanating a radioactive compound and thereby temporarily substantially eliminating the source of gamma rays, and applying a mixture of this compound with a radioactive-sensitive substance before the emanation and the emission of gamma rays has increased to a substantial amount.

In testimony whereof, I afiix my signature.

HERMAN SCHLUNDT. 

